Biodegradation of ethylene glycol was tested in a laboratory-scale, steady-state infiltration system of two arid region soil types by monitoring indigenous microbial growth after the infiltration of three concentrations of ethylene glycol. Microorganisms in the soils were able to adapt to the ethylene glycol in several cases, resulting in higher numbers of microorganisms and lower pHs in the effluents. These microorganisms were identified and were able to use ethylene glycol as a sole carbon source. The adaptation was seen best with high-moisture-content soils when the ethylene glycol concentrations were 1% or 10%. However, acclimation to 0.1% and 10% ethylene glycol did not occur in low-moisture-content clay soil, but did occur in low-moisture-content silt soil, indicating that soil type and moisture content are important factors. In all cases, microbial diversity decreased over time.